In the second group of qualitative analysis, `H_(2)S` is pass through a solution acidified with HCl in order to :

Options

A. limit the concentration of `S^(2-)` ions
B. increase the solubility of `H_(2)S`
C. increase the concentration of `S^(2-)` ions
D. provide extra `Cl^(-)` ions

Explanation

To solve the question regarding why `H2S` is passed through a solution acidified with `HCl` in the second group of qualitative analysis, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Dissociation of H2S**:
- Hydrogen sulfide (`H2S`) dissociates in water to produce hydrogen ions (`H+`) and sulfide ions (`S^2-`).
- The dissociation can be represented as:
\[ H2S \rightleftharpoons 2H^+ + S^{2-} \]

2. **Understanding the Dissociation of HCl**:
- Hydrochloric acid (`HCl`) also dissociates in water to produce hydrogen ions (`H+`) and chloride ions (`Cl^-`).
- The dissociation can be represented as:
\[ HCl \rightarrow H^+ + Cl^- \]

3. **Common Ion Effect**:
- When `HCl` is added to the solution, it increases the concentration of `H+` ions in the solution.
- This increase in `H+` ions leads to a common ion effect because both `H2S` and `HCl` release `H+` ions.

4. **Impact on H2S Dissociation**:
- According to Le Chatelier's principle, the addition of a common ion (`H+`) will shift the equilibrium of the dissociation of `H2S` to the left.
- This results in the suppression of the formation of `S^{2-}` ions because the system will try to counteract the increase in `H+` ions by favoring the formation of `H2S`.

5. **Conclusion**:
- Therefore, passing `H2S` through a solution acidified with `HCl` suppresses the dissociation of `H2S`, limiting the concentration of `S^{2-}` ions in the solution.

### Final Answer:
In the second group of qualitative analysis, `H2S` is passed through a solution acidified with `HCl` in order to suppress the dissociation of `H2S` due to the common ion effect, which limits the concentration of `S^{2-}` ions.

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